1. Field of the Invention
The present invention relates to the preparation of linear dicarboxylic acids, e.g., adipic acid, by hydrocarboxylating unsaturated monocarboxylic acids. e.g., 3-pentenoic acid, with carbon monoxide and water in the presence of a rhodium-containing catalyst, an iodide promoter and certain inert halocarbon solvents, e.g., methylene chloride.
2. Description of the Prior Art
U.S. Pat. No. 3,876,695, issued on Apr. 8, 1975 to Nicholaus Von Kutepow, discloses a process for the production of adipic acid by the reaction of butadiene, carbon monoxide and water using certain rhodium carbonyl complexes along with free or combined halogen as a catalyst system. The patentee discloses the advantage of using a solvent in the system which is a nonsolvent for adipic acid and cites as operable aromatic hydrocarbons, e.g., xylene, saturated cycloaliphatic hydrocarbons, e.g., cyclohexane and saturated aliphatic hydrocarbons, preferably those having 8-12 carbon atoms. The patentee suggests introducing catalyst in aqueous solution when practicing the process continuously. In Column 1, lines 10-50, the patentee discusses representative art on the preparation of acids and esters via carbonylation.
U.S. Pat. No. 4,172,087, issued on Oct. 23, 1979 to J. F. Knifton discloses a process for the carbonylation and concurrent dimerization of olefins such as 1,3-butadiene in the presence of hydroxylated coreactants, a dual function palladium catalyst and a tertiary nitrogen-containing base to produce acids and ester derivatives of unsaturated carboxylic acids. The reaction of butadiene is taught to produce 3-pentenoic acid and 3,8-nonadienoic acid and their corresponding ester derivatives. The patentees do not discuss the desirability and/or effect of conducting the reaction in the presence of a solvent. The catalyst system requires the presence of ligands of Group VB elements to stabilize the palladium salts. Included in these ligands are numerous phosphorus-containing compounds, e.g., bis(1,2-diphenylphosphino)ethane.
European Pat. No. 0075524, published on Mar. 30, 1983 and assigned to Rhone-Poulenc Chimie De Base, discloses a process for the preparation of beta, gamma unsaturated carboxylic acids by the carbonylation of conjugated dienes using a palladium catalyst with a halide promoter to produce the corresponding esters.
Japanese Pat. 92,913 (unexamined) published on July 23, 1979 discloses the carbonylation of lactones to carboxylic acids using a platinum group metal, e.g., rhodium, promoted with iodine compounds. The patentees do not recognize any criticality with respect to the amount of water present and employ acetic acid as a solvent.
The production of 3-pentenoic acid is discussed in an article by Imyanitov et al., Karbonili-rovonie Nenasyshchennykh Uglevodorodov (1968) 225-32, CA 71 216484, a portion of which disclosure appears in U.K. Pat. 1,092,694 published on Feb. 4, 1965. The reaction was studied in a pyridine solvent with cobalt carbonyl catalysts under a pressure of 120-500 atmospheres. The authors note that the order with respect to water changes from approximately zero where the reaction mixture comprises equal molar amounts of water to -1 order at a 13-fold excess of water. The preparation of the esters of 3-pentenoic acid using cobalt catalysts is disclosed in German Patent DE 3040432, published on June 19, 1981. Hydrocarboxylations employing rhodium catalysts are discussed in the article Mechanistic Pathways in the Catalysis of Olefin Hydrocarboxylation by Rhodium, Iridium, and Cobalt Complexes, D. Forster et al., Catal. Rev.--Sci, Eng. 23(1&2) pp. 89-105 (1981).
U.S. Pat. No. 3,579,552 discloses the use of rhodium catalyst with an iodide promoter to prepare carboxylic acids from olefins and other ethylenically unsaturated compounds. In Column 8, lines 31-42, the patentees disclose that an excess of water is beneficial to the reaction which, according to the teachings of the patent, is conducted using the olefins themselves or carboxylic acids as solvent. Example 9 demonstrates the employment of acetic acid as a solvent for the reaction of butadiene. In all cases a significant percentage of the products are branched.